This invention is in the field of data acquisition and processing systems. More particularly, it is concerned with apparatus and methods for detecting analog signals at spaced locations, coding these signals and transmitting them as trains of single bit digital pulses over a single pair of conductors to a distant recording unit, and compositing pluralities of said signals.
Still more particularly it concerns a system in which a plurality of separate detectors produce analog signals which are amplified, added to shifting functions of selected amplitudes and axis-crossing-coded and transmitted by a two conductor cable to a disc recording means, and there composited with succeeding repetitions of the signals.
While this invention is useful in the acquisition of any type of analog signals such as in the field of data collection, vibration analysis, sonar signaling, nuclear technology, and so on, it is also very appropriately useful in the area of seismic prospecting and as a matter of convenience will be discussed in that application.
In the prior art systems the seismic signals detected by the geophones have normally been transmitted by separate pairs of conductors to the recording unit. Here they are amplified in high gain, gain ranging amplifiers, multiplexed into sequential amplitude samples of successive traces, and digitized to fifteen or more bits, after which they are temporarily recorded on a magnetic tape loop. The next repetition of the elastic wave signal is processed in a similar way and successive amplitude measurements of a given trace at a given time are summed and the sum is again recorded on the magnetic tape loop.